1. Field of the Invention
The present invention relates to the production of nonoxide monolithic ceramic shaped articles, and, more especially, to the production of such ceramic shaped articles from organometallic precursors.
2. Description of the Prior Art
Nonoxide ceramic materials such as AlN, B.sub.4 C, SiC or Si.sub.3 N.sub.4 are generally produced at high temperatures (1,700.degree. to 2,500.degree. C.) by sintering under pressure, hot-pressing or hot isostatic pressing of the appropriate ceramic powders containing such additives as are required to improve the densification thereof. This technique presents a number of disadvantages:
(1) Homogeneous distribution of the additives in the powder intended as the matrix is difficult to achieve. Complex grinding processes or wet-phase chemical techniques have been proposed to the art to improve such homogeneity. Nevertheless, the presence of nonhomogeneous regions cannot be avoided and this may result in the formation of cracks in the final product shaped article by reason of nonuniform shrinking of the ceramic during sintering. Because of this, the reproducibility and the reliability of this technique is limited;
(2) Densification of the ceramic requires high temperatures, namely, high energy requirements and concomitant increased costs;
(3) Polycrystalline materials are produced after sintering; however, the interface of the particles considerably limits the physical and mechanical properties of the material, especially at high temperatures.